1. Field of the Invention
The present invention generally relates to the field of electrical circuits and systems. More particularly, the invention relates to circuits and systems utilizing a battery and/or a battery charger.
2. Background Art
A battery-powered electronic device, such as a cellular phone, a laptop computer, or an MP3 player, typically includes a power management unit (PMU) coupled to a battery. The PMU can include a battery charger and a number of voltage regulators for providing regulated power to the electrical circuits in the electronic device. In a conventional PMU, as soon as an external power source, such as a USB port on a computer or an AC power adapter, is coupled to the battery charger input of the PMU, the battery charger in the PMU will start to charge the battery and a capacitor that is coupled to the battery input of the PMU. When the battery has been charged to a voltage greater than a threshold voltage, the voltage regulators in the PMU are turned on, thereby providing power to the electronic device.
However, if a battery is not installed in the electronic device when the battery charger input of the PMU is connected to the external power source, the PMU battery charger will begin charging the capacitor that is coupled to the battery input of the PMU. When the capacitor voltage exceeds a threshold voltage, the regulators in the PMU are turned on, which turns on the electronic device. However, if the current drawn by the electronic device exceeds the limited charging current provided by the PMU battery charger, the voltage across the capacitor will drop below the threshold voltage, thereby causing voltage regulators in the PMU and, consequently, the electronic device to turn off.
When the voltage regulators in the PMU are turned off, the current drawn from the battery charger is reduced, thereby causing the capacitor voltage to rise above the threshold voltage and cause the PMU regulators and, consequently, the electronic device to turn back on. The undesirable on/off cycles can continue to repeat as long as a battery is not installed in the electronic device and the charger input of the conventional PMU is connected to an external power source. Among other problems, the undesirable on/off cycles can degrade a user's experience using the electronic device.